This bug was caused by making it so that non-embossed modifier icon
buttons could become an operator button and retain their red highlight
for disabled modifiers. The icon button needs emboss turned off, but
in earlier versions of Blender, `UI_EMBOSS_NONE` would be overridden
by animation or red alert states.
Instead of abusing "NONE" to mean "none unless there is animation or
red alert", this commit adds a new emboss flag for that situation,
`UI_EMBOSS_NONE_OR_STATUS`, which uses no emboss unless there is an
animation state, or another status. There are only a few situations
where this is necessary, so the change isn't too big.
Differential Revision: https://developer.blender.org/D9902
6942dd9f49